Interpretive Summary: The mold Aspergillus parasiticus is a potent producer of aflatoxins, highly carcinogenic compounds that contaminate various agricultural commodities. In this paper we describe the newly discovered sexual stage of the mold. The sexual stage accounts for much of the variation in A. parasiticus populations in the field and will be an important factor in devising new strategies for controlling aflatoxin contamination.

Technical Abstract:
The sexual state of Aspergillus parasiticus, a potent aflatoxin-producing fungus within section Flavi, is described. The production of nonostiolate ascocarps surrounded by a separate peridium within the stroma places the teleomorph in the genus Petromyces. Petromyces parasiticus differs from P. alliaceus by its larger ascospores with finely tuberculate ornamentation. The anamorphic Aspergillus states of the two species differ in conidial head color and microscopic characters.